Trusty: Flickering problem with xorg opensource driver on ATI RV710 [Mobility Radeon HD 4330/4350/4550] [1002:9552]
Solution 1:
One of my laptops has the same problem.
The workaround for me is NOT to use any kernel above version 3.13.x-xx
(see the launchpad bug about this: https://bugs.launchpad.net/ubuntu/+bug/1479136 )